Hollow, cooled airfoils are well known in the art. They are used extensively in the hot turbine section of many of today's gas turbine engines to maintain metal temperatures within acceptable limits. It is desirable to cool the airfoil to an acceptable level using a minimum mass of coolant flow. This is accomplished by a variety of techniques including film, convective, and impingement cooling. Often the interior of the airfoil is a cavity extending from the leading to the trailing edge and from the root to the tip; and that cavity is divided, by ribs, into a plurality of spanwise extending channels which receive a flow of coolant therein from passages within the root of the airfoil. The ribs are used to create a pattern of flow passages within the airfoil to cause, for example, the same unit mass of coolant to traverse a large area of the internal wall surface to maximize use of its cooling capacity.
In the airfoil shown in U.S. Pat. No. 4,514,144 to Lee, individual, separate spanwise coolant passages carry coolant into heat exchange relationship to the leading and trailing edge, respectively. Each of those channels is fed from a separate coolant passage through the root. The remainder of the airfoil is cooled by a single serpentine channel which carries coolant fluid received from yet another passage through the root. The serpentine channel comprises a plurality of adjacent spanwise extending legs in series flow relation, with the rear-most leg first receiving the coolant fluid. The fluid passes across the spanwise length of the blade in serpentine fashion to the front-most leg and exits through film cooling holes through the airfoil sidewalls, which holes intersect the channel legs. Hollow airfoil coolant configurations somewhat similar to the Lee configuration are shown in U.S. Pat. No. 3,628,885 and Japanese Pat. No. 58-170801 issued Nov. 7, 1983. The former, like Lee, includes a five-pass serpentine channel, while the latter describes a three-pass serpentine channel.
U.S. Pat. No. 3,533,711 shows an airfoil having a pair of serpentine channels, each receiving a separate flow of coolant from a common plenum below the blade root. The inlet legs of the serpentine channels are parallel and adjacent each other and are located centrally of the airfoil. The coolant flow in the rear-most serpentine channel traverses the span of the airfoil as it travels toward and ultimately cools and exits the trailing edge of the airfoil. The coolant flow within the front-most serpentine channel traverses the span of the airfoil as it moves toward and ultimately cools the leading edge of the airfoil.
In U.S. Pat. No. 4,073,599 the airfoil coolant cavity is also divided into a pair of separate serpentine channels; however, the coolant is introduced into the front-most serpentine channel via its leg nearest the leading edge. That fluid travels toward the trailing edge as it traverses the span of the airfoil, and it exits the airfoil from its rear-most leg, which leg is centrally located within the airfoil cavity and immediately forward of and adjacent the other serpentine channel.
While the prior art configurations may perform adequately for the applications for which they were designed, newer applications are becoming more and more demanding, requiring the development of more efficient cooling configurations for airfoils which need to operate in even hotter environments. At the same time demands are being made to minimize airfoil weight and the amount of coolant needed to do the job.